The present invention relates to a process for the preparation of end-products for external use, made of acrylic fibre, which uses a copolyamide adhesive resistant to solar light.
Covers or sun shields, such as for example external awnings, are preferably made of acrylic fibre, either raw or dyed with pigments, which are extremely stable to solar radiation.
Preference for the use of acrylic fibre for the preparation of end-products exposed to the sun is due to the exceptional resistance of this fibre to solar radiation.
Whereas other fibres such as those deriving from polypropylene, cotton, polyester, etc., undergo a considerable deterioration in toughness after a few months of exposure to light, acrylic fibres remain unaltered and maintain almost all of their initial toughness after several years of exposure.
Pigments can be incorporated into acrylic fibres, which, if suitably selected, enable the mechanical resistance and the original brightness of the colours of the fibres to remain unaltered.
In order to produce end-products for external use having the desired dimensions, it is necessary to join sheets of acrylic fibre. This operation is typically effected with traditional seaming systems using threads of various materials, preferably of polyester or polyamide.
This system however, in addition to having a limited duration over a period of time for the parts of sewing threads exposed to solar radiation, also presents the problem of costs and thickness of the junctions.
The borders of the sewn sheets are, in fact, folded inwards and this increases the thickness of the sewn parts increasing the bulk when the awning is rolled up.
Under conditions of humidity or water absorption, the rolled-up awning is subject to greater stress on the area of the junctions and, as a result of the heat deriving from solar radiation, produces permanent and visible deformations, when the awning is unrolled, in the form of unaesthetic undulations.
For these reasons, a system has been studied for joining the borders of the sheets by means of adhesives.
Adhesives consisting of polyacrylates, synthetic rubbers, vinyl polymers, polyesters, polyurethanes, etc., are generally used, applied alone or with organic solvents.
These joining systems however have proved to be difficult to effect for the following reasons:
1. the use of organic solvents such as toluene, chlorinated hydrocarbons, acetone, etc. requires, during processing, the use of aspiration systems to limit their toxicity and can also give rise to fires, explosions, etc.
2. these adhesives have a lower mechanical resistance than that obtained with the traditional seaming system and they are not stable to solar exposure or weather-proof.
It has now been found, according to the present invention, that it is possible to overcome the drawbacks of the known art discussed above, by using a copolyamide adhesive for joining the borders of acrylic cloth. The use of this adhesive provides substantial advantages, in particular:
1. a mechanical resistance equal to or higher than that of traditional seaming systems;
2. a high resistance to light in terms of yellowing resistance and conservation of toughness;
3. a high physico-chemical affinity for the acrylic fibre which allows perfect wettability of the surface of the end-product, on the part of the adhesive, which results in the exceptional tensile strength of the junctions.
In accordance with this, the objective of the present invention relates to a process for the preparation of end-products for external use which comprises the joining of one or more sheets made of fabric essentially consisting of acrylic fibres by means of a copolyamide adhesive, the above junction being effected by applying said adhesive to the acrylic matrix by melting, with subsequent pressing in the glued area by means of a system capable of exerting an adequate pressure.
Copolyamide adhesives suitable for the purposes of the present invention are preferably selected from those consisting of a polyamide terpolymer based on 6/6.6/12 nylon and have the following characteristics:
melting point ranging from 115-130xc2x0 C.;
glass transition temperature ranging from 15 to 20xc2x0 C.;
viscosity of the molten product at 2.16 kg/160xc2x0 C. ranging from 150 to 700 Pa.s.
These adhesives can be prepared with the known techniques and are also commercially available.
The adhesive, in powder form, can be used in aqueous dispersion in the form of a spreadable paste and is applied to the edge of one of the two sheets with subsequent pressing and melting of the adhesive by heating to about 150xc2x0 C.
Alternatively, the adhesive in powder form is fed to a device heated to the melting point of the polymers and is spread, in a fine layer, on the edge of the fabric.
As the molten adhesive is applied on a layer of the fabric, the edge of the other sheet of fabric is overlapped, exerting a pressure which is sufficient to allow adhesion of the borders of the fabric.
For this purpose, calenders, flat plates or other devices capable of exerting adequate pressure, can be used.
The end-products for external use obtained using these adhesives have proved to be more resistant than those obtained using adhesives with a greater nominal mechanical resistance, for example adhesives based on copolyesters, but with a poor affinity with the acrylic fibre.
For these end-products, the thickness in the overlapping area of the edges is the sum of the thicknesses of the single sheets in addition to a negligible thickness of the molten adhesive. The width of the overlapping area of the two sheets glued by the copolyamide adhesive is in relation to the adhesion strength required.
The following examples are illustrative but do not limit the scope of the invention described.